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--Of all the
attributes of eating quality, tenderness is rated the most important
factor affecting beef palatability--
Slow cooked
meals are generally easier to make and very cost effective using
cuts of meat that improve in texture and flavor when cooked for
long periods of time at low temperatures. These tough cuts of
meat contain large amounts of collagen which require long cooking
times to break down into a rich gelatin.
HOW DOES
SLOW COOKING WORK?
When you cook,
collagen begins to melt at about 160F and turns to a rich liquid,
gelatin. This gives meat a lot of flavor and a wonderful
silky texture. When cooking it is important to liquify collagen.
Denaturation of the collagen molecule is a kinetic
process, and hence a function of both temperature and duration
of heating. Cooking at low temperatures require long periods of
time to liquify collagen.
COOKING
MEAT TEMPERATURES
105F/40C
- 122F/50C
--Calpains begin to denature and lose activity till around 105F,
cathepsins at 122F. Since enzyme activity increases up to those
temperatures, slow cooking can provide a significant aging effect
during cooking.
| Increased
activity of enzymes calpains and cathepsin disrupt myofibrils
and will produce more tender meat. Calpains, which are stored
in the cytosol near Z-lines require calcium to be activated,
Cathepsins, are stored in lysosomes. Calpains work on Z-lines
while cathepsins work on actin-myosin bonds. |
Note: Meat
should however be quickly seared or blanched first to kill surface
microbes.
120°F/50°C
-- Meat develops a white opacity as heat sensitive myosin
denatures. Coagulation produces large enough clumps to scatter
light. Red meat turns pink.
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Rare
Meats: 120°F/50°C is the early stages of juiciness
in meats as the the protein myosin, begins to coagulate
. This lends each cell some solidity and the meat some firmness.
As the myosin molecules bond to each other they begin to
squeeze out water molecules that separated them. Water then
collects around the solidifyed protein core and is squeezed
out of the cell by connective tissue. At this temperature
meat is considered rare and when sliced juices will break
through weak spots in the connective tissue
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140°F/60°C
-- Red myoglobin begins to denature into tan colored hemichrome.
Meat turns from pink to brown-grey color.
140°F/60°C
-- Meat suddely releases lots of juice, shrinks noticebly,
and becomes chewy as a result of collagen denaturing which squeezes
out liquids.
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Medium
-- Well Meats: Collagen shrinks as the meat tmeperature
rises to 140/60 more of the protein coagulates and cells
become more seggregated into a solid core and surrounding
liquid as the meat gets progressively firmer and moister.
At 140-150 the meat suddenly releases lots of juices, shrinks
noticeably and becomes chewier as a result of collagen shrinkage.
Meat served at this temperature is considered medium and
begins to change from juicy to dry.
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160°F/70°C
-- Connective
tissue collagen begins to dissolve to gelatin. Melting of collagen
starts to accelerate at 160F and continues rapidly up to 180F.
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Well
Done Slow Cooked Meats: Falling apart tenderness collagen
turns to gelatin at 160/70. The meat gets dryer, but at
160F the connective tissues containing collagen begins to
dissolve into gelatin. With time muscle fibers that had
been held tightly together begin to easily spread apart.
Although the fibers are still very stiff and dry the meat
appears more tender since the gelatins provide succulence.
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NOTES:
At 140°F
changes are caused by the denaturing of collagen in the cells.
Meat served at this temperature med-rare is changing from juicy
to dry. At 160°F/ 70°C connective tissue collagen
begins to dissolve to gelatin. This however is a very lengthy
process. The fibers are still stiff and dry but meat seems more
tender. Source: Harold McGee -- On Food and Cooking
Anatomy
of muscle fiber
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A
muscle is completely enclosed by a thick sheath of connective
tissue (the epimysium) and is divided into bundles of fibres
by a connective tissue network (perimysium). Individual muscle
fibres are bounded by a plasma membrene surrounded by connective
tissue (endomysium) which consists of a basement membrane
surrounded by a reticular later in which a meshwork of fine
collage fibrils is embedded in a matrix. Tendons are elastic
collagenous tissues. |
| Source:
Wikipedia |
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Scattered
among the muscle fibers are fat cells which store energy for the
muscles. Fat is crucial to meat texture. Waxy when it is cold,
fat does not evaporate when you are cooking as does water. It
melts and lubricates the fibers as they are getting tougher under
the heat. Fat is also the source of much of the flavor in meat.
As the animal ages the flavor compounds build up and get stronger.
After the animal is slaughtered, the fat can turn rancid if stored
improperly or too long.
THE CHALLENGE IN COOKING MEAT
We
like our meat tender and juicy at the same time...
We therefore
want our meat to be cooked tender where tough collagen is converted
to gelatin but with a minimum loss of moisture. The reality is
that these methods are contracdictory and hence the challenge
or dilemma to cooking meats. To minimize moisture loss requires
temperatures less than 130F, however .turning collagen into gelatin
requires temperatures above 160F and for extended time periods.
As moisture
evaporates, the meat begins to shrink. A slab can lose 20% or
more of its weight in cooking due to shrinkage. Even meat cooked
in liquid will dry out although not as quickly. So we are faced
with a dilemma. To liquefy the collagen we need to cook the meat
to 180F and hold it there for for long periods of time. But by
then it is well past well-done and the muscle fibers can be dryed
out. As a result, we need to add moisture.
How to
slow loss of moisture
Brining.
Brining adds a significant amount of moisture, it helps
retain moisture during cooking, contributes noticeable flavor
enhancements.
Steaming.
Another method of adding moisture is to cook the meat
in very high humidity by wrapping it in foil with a little water
or juice. This keeps moisture from escaping and some vapors penetrate
the meat.
Braising
or poaching (--low temperatures--). Braising
is a method of cooking by submerging the meat in hot liquid, but
not hot enough to boil. Braising can give you juicy, tender, and
flavorful meat, especially if you use a flavorful braising liquid.
But it tends to pull all the collagen out and rob the meat of
its natural flavor. Flavor the liquid (water with pickling spices
is a nice simple start), completely submerge the slab, keep the
lid off, keep the temp down to about 160-180F for about 30 minutes,
and let the meat cool in the liquid for 20-30 minutes so it will
absorb some of the water before putting it on the grill.
Breakage
of collagen covalent links using Acids -- (Tenderizing meats with
acid) -- It
is well known that adding a little vinegar to a stock will help
tenderize meat while cooking. It is also useful to marinate meat
for a few hours using vinegar to tenderize meat. Offer and Knight
(1988) suggested that one of the mechanisms of pH induced tenderisation
of meat could be a breakage of covalent collagen cross-links and
of some specific peptide bonds.
Here are
tips to keep in mind when slow-low roasting:
- Develop
a caramelized crust before slow cooking -- by searing
the meat either in a dry pan or with a small amount of oil
or fat.
- Place
the meat or roast fat side up in the pan so it self-bastes.
- Tenderize
your cuts of meat --e..g, pounding meat, buying aged meats
(Note: meats cooked longer a 120F will age and be more tender),
marinading meats with acids with tenderize the meat.
- Tent
the resting meat with foil and allow 10 to 15 minutes
before cutting it so the meat's juices will return to the
center; slice the meat against the grain.
References
Review:
Collagen contribution to meat toughness: Theoretical aspects
Jacques Lepetit ..Meat Science 80 (2008) 960–967
Offer,
G., & Knight, P. (1988). The structural basis of water-holding
in meat. Part 1: General principles and water uptake in meat
processing. Developments in Meat Science, 4, 63–171.
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